Holley oil pan blues

[cornerstone]

I’ve already installed a aluminum Holley 302-20 oil pan on my L83 and the drain plug that was with the kit is too small, it is an M12x1.75.

I called Holley to find out what size bolt the drain hole was tappped for, and the tech guy didn’t have a clue. He offered to exchange the whole oil pan kit but I really don’t feel like taking it off of the engine repackaging everything and going through the hassle of sending it back. I just want to buy a drain plug that will fit. It appears to be an M14x1.75 or M14x2.0 and neither of these are available.

I found the closest SAE version...a 1/2”x13 tpi bolt and added a Teflon washer. It was a bit loose but seemed like it would hold a seal...
I added the oil and noticed a drip, so I gave the brain bolt a little more torque and this bolt is still to small, as it will not grab enough material to hunker down.

So.... my next idea is to drill and tap a larger size and move forward, but something in me cringes when I have to modify a brand new $325 part.
If I do drill and tap new threads I’m thinking that would go to a 9/16 bolt. Should I go with a fine thread (20 tpi) or a coarse thread (12 tpi)? I have both taps already.

Any idea where I can get an M14 flange bolt with a 1.75 or 2.0 pitch?
Any suggestions before I cut new threads in this BRAND NEW oil pan?!!

The plug on the right is what they provided, and the one in the left is a 1/2”x 13 tpi bolt. Both are too small.